Isomorphisms of triform semigroups
Kenneth D. Magill · Journal of the Australian Mathematical Society · 1969
For any point x, we use the symbol x to denote {(x, x)}. By a triform, we mean a triple (X, Fx, S[X]) where X is a nonempty set, Fx is a family of subsets of X, [X] is a family of subsets of X x X and the following conditions are satisfied: .